The present invention relates to process transmitters, such as transmitters which provide an analog or digital output over a pair of wires as a function of a measured absolute or differential pressure. In particular, the invention relates to transmitters to be used in environments of high electromagnetic interference (EMI) and which have circuitry which includes an actuatable switch for modifying a parameter of the circuit such as a zero or span setting.
Transmitters having circuitry disposed in a housing and protected by an outer cover are known. It is also known to include one or more actuatable switch for adjusting a parameter of the circuit, the actuatable switch being accessable only after removal of the outer cover. The present invention includes an electrically conductive inner cover having a sleeve in frictional contact with electrically conductive walls of the housing to reduce effects of EMI when the outer cover is removed, and simultaneously to permit operator access to the actuatable switch while the circuit is energized. EMI can result from electromagnetic waves broadcast from, for example, a radio communicator used by the operator.